Furnace control apparatus



June 12 1945.

D. J. MOSSHART FURNACE CONTROL APPARATUS Filed Oct. 7, 1943 INVENTOR -Dona/J d Moss/mt ATI'ORNEY structural members in the form of I beams extend from front to rear of the-furnace and Patented June 12, 1945 Donald J.

Mosshart, Ar

dmore, Pa.,' assignor to Westinghouse Electric corporation, East Pittsburgh, Pa.,

Application October 7,

This invention relates to furnace controls, more particularly to means for controlling the flow of air through the fuel bed within the-furnace, and

has for an object to provide improved control invention as will be apparent from the following description and claims taken in connection with the accompanying drawing, forming a part of this application, in which:

Fig. 1 is a horizontal sectional view through a furnace embodying the present invention;

Fig. 2 is a transverse sectional view of the furnace shown in Fig. 1, illustrating schematically control means constructed in accordance with the invention; and,

Fig. 3 is an enlarged fragmentary detail view of a modified construction.

Referring now to the drawing more in detail, the numeral l indicates, in its entirety, a furnace comprising front and rear walls H and I2, respectively, and side walls IS, the furnace having a plurality of grate bars [4 of the inverted, obtuse V-type disposed therein to provide a fuelsupporting surface extending substantially from wall to wall.

A rotary impeller l5 from the hopper l6, through the furnace front wall ll, onto the central portion of the grate surface, in a path extending from the furnace front wall II to the rear wall l2, but spaced from the side wall l3, as best illustrated in Fi 1.

A pair of masonrywalls l9, surmounted by support the terminal portions of the grate bars thev space beneath the grate bars. A horizontal partition 2i cooperates with a pair of interme diate partitions 22, .in the form of ,I-beams, to divide the space chambers B. It will be noted that the intermediate ll-beam part'tions 22 provide supports for throws or sprinkles fuel an opening l'l in I dampers 25 4 the shaft 34 and a corporation'of Pennsylvania 1943, Serial No. 505,303

9 Claims. (Cl. 110-32) the grate bars intermediate their -tions.

Primary air is supplied to the plenum chambers A and B by suitable means, such as the blower 24, the volume of air being controlled by and the air being admitted to the plenum chambers through the fixed orifices 26 and 21, formed in the horizontal partition 2i. In order that equal pressures may be obtained in the two side plenum chambers B, there is provided a pressure balancing duct 28, providing communication between the plenum chambers.

The fuel deposited upon the grate'bars l4, by the rotary impeller I5, is limited substantially to the area of these bars overlying the central plenum chamber A, and the fuel so deposited thereonis fed'laterally over the end portions of the grate bars overlying the plenum chambers B, to the dump plates 29, by transverse reciprocation of alternate grate bars. Such reciprocation of alternate grate bars is provided for by the following described mechanism: A suitable engine, such as the fluid motor 3|, imparts reciprocatory motion to the rod 32, connected at its free end to the lower end of the double-ended arm 33, mounted for free rotation upon the shaft 34, which extends from front to rear of the furnace. The upper end of the arm 33 carries a pivotally-mounted dog or pawl 35 the teeth 36, formed about the 31, which is fixedly secured adapted to engage periphery of the disc 38 is likewise flxedly.secured to is connected by link 39 to the rocker arm 40 of the shaft 4|. The latter is provided with an upstanding rib 42 extending throughout its length and adapted to have its free edge received between the bifurcations of the lugs 43, which depend from the alternate reciprocable grate bars l4. It will be obvious that this mechanism provides for transverse reciprocation of the alternate grate bars, the remaining A crankarm grate bars being stationary upon their supportthe portions of the grate ll The wall members i! and serve to-enclose beneath the grate bars into a central plenum chamber A and side lplenuin mg structure, this reciprocation'of alternate bars providing for progressive bars overlying the central plenum chamber A, over the end surfaces of the grate bars overlying the plenum chambers B, to the dump plates 29, from which the ash and 'refuse 'may be periodically dumped in the usual manner.

In order to control the rate of the progressive feed of fuel from the central to the sideportions of the grate surface, to maintain a fuel bed of terminal por- I the central portion of feed of the fuel from desired relative thickness, there is provided the control mechanism now to be described.

A pair of diaphragm chambers 46 and 41 are in communication with the interiors of the plenum chambers A and B, respectively, through the conduits 48 and 49, respectively. Depending rods 50 and connect the diaphragms 48 and 41, respectively, with opposite ends of the bar 52, pivoted at 53 intermediate its ends on the fixed support 54. The bar 52 is provided with a plurality of pivot openings 55 in order that the location of the pivot point of the bar may be adjusted to obtain the desired action thereof. One end of the bar 52 is provided with a depending rod 55, pivotally connected to an arm 51 of a bellcrank, pivotally mounted, at 58, on a fixed support 59. The other arm 60 of the bellcrank carries a mercury switch 8| for opening and closing the electrical circuit 52, this circuit controlling action of the solenoid 63, which is connected by the spring 64 to the pawl 35 of the grate bar reciprocating mechanism. Closing of the circuit 62 will operate the solenoid 63, to tension the spring 64, thereby applying a force tending to withdraw, or disengage, the pawl 35 from the toothed disc 31. However, the spring 64 permits the pawl to remain inrengagement with the teeth until the driving movement of the arm 33 has been completed.

As soon as the arm 33 starts its return movement,

the engaging pressure between the pawl and the teeth 36 will be relieved and the spring will withdraw the pawl from its engagement with the teeth.

In operation, it is desired that the flow of air through the layer of fuel over central plenum chamber A bears some predetermined fixed relation to the flow of air through the layer of fuel over side'plenum chambers B. Since chambers A- and B receive air through orifices froma comv mon pressure P1, the pressures P2 and Pa in chambers A and B, respectively are a function of the rates offlow through these chambers tov the fire. Therefore, the ratio of pressure P: to; pressure P: is a measure of the relation between the rates of flow to the two portions of the fire.

If the layer of fuel over the central-plenum chamber A becomes so thin, or the layer of fuel over side plenum chambers B'becomes so thick that the flow of air through chamber A is greater than desired in' rela tion to the flow through chambers B, the pressure P2 in chamber A will drop below the desired value in relation to. pressure P3 in chambers B. This change in the pressure differential. ill afie'ct the diaphragm 48 and 41 to cause downward. movement of that end of the bar 52 carrying the depending rodv 56, with the result that the bellcrank is moved to a position where themercury switch Slcloses the circuit 62, thereby energizing the solenoid 61 to disengage the pawl from the toothed disc 31, thus interrupting the reciprocation of the grate bars l4. Thereupon, fuel bed deposited upon the central portion of the grate surface will increase in thickness inasmuch as no fuel is being moved therefrom to the side portions, and, at the same time, the fuel remaining on the side portions will be reduced in thickness by combustion so that the original desired relation of air pressure between the plenum chambers A and B will be quickly reestablished. As soon as the pressure differential has changed to the opposite direction, the diaphragn'is will reactto break the circuit 82, deenergizing the solenoid 53 and re-establishing the drive to reciprocate the grate bars, whereupon the fuel will again be progressively fed from the in the resistance of the fuel bed to flow of air therethrough. Thus, the fuel bed functions as a variable discharge orifice for the chambers therebelow.

Flow through the first and the second (fuel bed) orifices are functions of the pressure drops, and as long as the orifices do not change, P2 and P3 remain constant. However, if the second orifice (fuel bed) changes, the pressures Pa and P: required to maintain the flow change, the pressures P2 and Pa increasing with reduction in the second orifice area and vice versa. Increase in the sec- ,ond orifice area means that, for the same flow,

P2 and P3 can be lower; but if P: and P: are lower, the pressure drop from P1 to P: and P: is increased, causing greater flow through the first orifice.

In Fig. 3, there is illustrated a modification of the previously described control means, wherein the drive between the pawl and toothed disc may be merely reduced, instead of completely interrupted, upon the occurrence of a change in the pressure relationship of the two plenum chambers.

In this modification the bellcrank arm 55, instead of operating a mercury switch to control an electric circuit, is directly connected to a blocking bar 10, whose free end is adapted to overlie a plurality of the teeth 38 on the disc 3'8, to control the number. of such teeth engaged by the pawl 35 during each complete movement of the arm 33. Thus, upon occurrence of a slight change in the pressure diflerential between the plenum chambers A and B,.the bellcrank arm bl! will move the bar I0 suificiently to cover only a few vented from engaging the teeth covered thereby. Under extreme conditions of pressure change, the

bar 10 would prevent engagement of the pawl with any of the teeth 36, thereby completely interrupting operation of the bar reciprocating mechanism.

While the invention has been shown in several forms, it will be obvious to those skilled in the art that it is not so-limited, but is susceptible of various other changes and modifications without departingfrom the spirit thereof, and it is desired,

- tion of said surface, means for progressively feeding the deposited fuel from said one portion of the fuel-supporting surface to another portion 'thereof, and means for interrupting and initiating said progressive feed in response to changes sive to changes in the diflerence in pressure within the relative resistances of the beds of fuel on said portions to flow of air therethrough.

2. In a stoker, means providing a fuel-supporting surface, means for feeding fuel to a first portion of said surface, means for progressively feed- .ing said fuel from said first portion to a second portion of the fuel-supporting surface, and means for decreasing the rate of said progressive feed ing in response to decrease in the resistance of the fuel on the first portion of the fuel-supporting surface to flow of air therethrough.

3. In a stoker, means providing a fuel-supporting surface, means for feeding fuel to a first portion of said surface, means for progressively feeding said fuel from said first portion to a second portion of the fuel-supporting surface, and means for increasing the rate of said progressive feedtions to flow of air therethrough.

'5. Apparatus of the character described, comprising means providing a fuel-supporting surface, means cooperating with said first-mentioned means to provide below the latter a pair of chambers, means for feeding fuel toa first portion of the fuel-supporting surface overlying one of said chambers, means; for progressively feeding fuel from said first portion to a second portion of the'fuelsupporting surface overlying the other of said pair of chambers, means for admitting constant ratios of volumes 'of air to each of. said chambers for discharge through the bed of fuelthereabove, and means for varying the rate of second portion of the fuel-supporting surface in response to variations in the pressure differential between the interiors of the pair of chambers.

6. Apparatus of .the character described, comprising means providing a. fuel-supporting surface; means cooperating with said first-mentioned means to provide below the latter a pair of cham bers; means for feeding fuel to that portion of the fuel-supporting surface which overlies one of the chambers; means for progressively feeding said fuel from said portion of the fuel-supporting surface to the portion overlyingthe other of said 4 in the pressure differential between said first and the progressive-feed of fuel from the first to the in the two chambers, which changes result from variations in the resistance of the fuel thereabove to flow of air therethrough, for varying the rate of progressive feed of fuel from the one to the other portion of the fuel-supporting surface.

7. Apparatus of the character described, comprising a plurality of grate members-providing a fuel-supporting surface; means providing a pair of chambers beneath said grate members; means for feeding fuel to a first portion of the fuelsupporting surface ,overlying one of said chambers; means for progressively feeding said fuel from said first portion of the fuel-supporting surface to a second portion thereof ooverlying the other of said chambers; means for supplying metered air at superatmospheric pressure to the chambers for flow therefrom through the fuel thereabove; and means responsive to variations in the pressure differential between the two chambers, which variations result from changes in the resistance of the fuel thereabove to fiow of air therethrough, for controlling the progressive feed of fuel from the firstto the second portion of the fuel-supporting surface. v

8. Apparatus of the character described, comprising a plurality of grate members providing a fuel-supporting surface; side and bottom wall structure supporting said grate members and cooperating therewith to define an enclosure therebelow; partition structure dividing the space.

within said enclosure into two or more-cham bers;"means for feeding fuel to a first portion'of the fuel-supporting surface overlying a first one feed the fuel from said first portion of the fuel-' supporting surface to a second portion thereof overlying a second one of the chambers; means for admitting a constant supply of air to each of the chambers; and means responsive to changes second chambers for controlling the means for imparting motion to the grate members.

9. Apparatus of the character described comprising means p'roviding a fuel-supporting surface, means cooperating with said first-mentioned means, to provide below the latter a. chamber, means for feeding fuel to the fuel-supporting surface to form thereon a fuel bed overlying said chamber and providing a. variable discharge orifice therefrom, means providing an inlet orifice to the chamber, means for supplying air to said chamber through the inlet orifice at' constant 86- pressure, and means responsive to change in pres- 4)! the rue! bed above said chamber.

DONALD J. MOBSHART. 

